1. Technical Field
The present invention relates to interconnect structures, and more specifically relates to a receptor pad for use in a chip carrier package.
2. Prior Art
Forming electrical connections between components remains an ongoing challenge in the electronics industry. As sizes decrease, more precision and smaller interconnections are required when attaching components to circuit boards, planar surfaces, substrates, and the like (collectively referred to herein as xe2x80x9clanding areasxe2x80x9d). While soldering techniques are widely available to connect components, the ability to provide landing areas with small and reliable receptor pads becomes increasingly difficult.
One particular application that utilizes high density interconnections involves integrated circuit (IC) chip packaging. An IC chip package comprises a relatively small IC device encapsulated in a larger package, which is more suitable for use in the industry. The xe2x80x9clargerxe2x80x9d IC chip package includes external connectors (e.g., a ball grid array) suitable for electrical communication with a traditional circuit board. Conversely, the smaller IC device, which comprises much smaller connectors, resides within the IC chip package on a landing area or laminate. Thus, the IC chip package must provide a relatively small landing area as well as a system for internally routing signals between external package connectors and internal IC device connectors.
In order to achieve this redirection of signals, a landing area comprised of a circuitized substrate or laminate is provided having a set of internal (high density) receptor pads. Circuit lines within the substrate route the signals from external connectors, which are in communication with external devices, to the receptor pads on a landing area, which connect with the IC device. Connection between the landing area and IC device is generally achieved by soldering. Solder techniques are well known in the art and examples are found in U.S. Pat. No. 5,597,469 issued on Jan. 28, 1997 to Carey et al., and assigned to International Business Machines.
As noted, given the trend towards smaller IC devices, the circuitized substrate must provide a high number of receptor pads in a very small surface area. This is becoming more difficult to achieve with present design techniques. Specifically, because solder cannot wet down onto non-metal and/or organic materials, receptor pads must be designed with an adequate metal surface to ensure attachment. If such a surface is not provided, solder often fails to properly wet the pads and becomes inadvertently removed from the pad during subsequent reflow and wash processes. The most common pad structure to ensure adequate metal surface comprises a xe2x80x9cdog bonexe2x80x9d structure that utilizes a flat pad attached to an adjacent via. Unfortunately, these structures take up a lot of surface area.
Thus, a need exists to provide a receptor pad that can reliably receive solder without requiring an extensive amount of surface area. All of the aforementioned references are hereby incorporated by reference.
The present invention provides a method for forming a receptor pad on a laminate, comprising the steps of: providing a circuitized substrate that includes a surface having a conductive element; mounting an external dielectric layer (EDL) on the surface; forming an opening in the EDL to expose the conductive element and create a microvia; treating an interior side wall surface of the microvia to promote copper adhesion; and electroplating the microvia with copper.
Once the microvia is electroplated, a resist process is used to define and finalize the receptor pad. Thereafter, a wet solder paste may be deposited on the receptor pads followed by a reflowing and washing step to create a reliable solder bump.
The invention also comprises a laminate having a receptor pad formed thereon, comprising: a circuitized substrate having a conductive element on a surface; an EDL mounted on the circuitized substrate, the EDL having an opening positioned above the conductive element to form a microvia; and an electroplated layer deposited within the microvia.
It is therefore an advantage of the present invention to provide a microvia structure that can be used as a receptor pad and directly receive a solder deposit.
It is therefore a further advantage of the present invention to provide higher density surface mounting technology by eliminating the need for dog bones and the like.
It is therefore a further advantage of the present invention to provide a microvia that allows solder to reliably wet thereon.